This is a note to let you know that I've just added the patch titled
x86/pti: Make unpoison of pgd for trusted boot work for real
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: x86-pti-make-unpoison-of-pgd-for-trusted-boot-work-for-real.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From hughd@google.com Mon Feb 5 04:59:38 2018
From: Hugh Dickins hughd@google.com Date: Mon, 29 Jan 2018 18:17:26 -0800 Subject: x86/pti: Make unpoison of pgd for trusted boot work for real To: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Dave Hansen dave.hansen@linux.intel.com, Thomas Gleixner tglx@linutronix.de, Jon Masters jcm@redhat.com, Tim Chen tim.c.chen@linux.intel.com, gnomes@lxorguk.ukuu.org.uk, peterz@infradead.org, ning.sun@intel.com, tboot-devel@lists.sourceforge.net, andi@firstfloor.org, luto@kernel.org, law@redhat.com, pbonzini@redhat.com, torvalds@linux-foundation.org, gregkh@linux-foundation.org, dwmw@amazon.co.uk, nickc@redhat.com, stable@vger.kernel.org, Jiri Kosina jkosina@suse.cz, Hugh Dickins hughd@google.com Message-ID: 20180130021726.229367-1-hughd@google.com
From: Dave Hansen dave.hansen@linux.intel.com
commit 445b69e3b75e42362a5bdc13c8b8f61599e2228a upstream
The inital fix for trusted boot and PTI potentially misses the pgd clearing if pud_alloc() sets a PGD. It probably works in *practice* because for two adjacent calls to map_tboot_page() that share a PGD entry, the first will clear NX, *then* allocate and set the PGD (without NX clear). The second call will *not* allocate but will clear the NX bit.
Defer the NX clearing to a point after it is known that all top-level allocations have occurred. Add a comment to clarify why.
[ tglx: Massaged changelog ]
[ hughd notes: I have not tested tboot, but this looks to me as necessary and as safe in old-Kaiser backports as it is upstream; I'm not submitting the commit-to-be-fixed 262b6b30087, since it was undone by 445b69e3b75e, and makes conflict trouble because of 5-level's p4d versus 4-level's pgd.]
Fixes: 262b6b30087 ("x86/tboot: Unbreak tboot with PTI enabled") Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Andrea Arcangeli aarcange@redhat.com Cc: Jon Masters jcm@redhat.com Cc: Tim Chen tim.c.chen@linux.intel.com Cc: gnomes@lxorguk.ukuu.org.uk Cc: peterz@infradead.org Cc: ning.sun@intel.com Cc: tboot-devel@lists.sourceforge.net Cc: andi@firstfloor.org Cc: luto@kernel.org Cc: law@redhat.com Cc: pbonzini@redhat.com Cc: torvalds@linux-foundation.org Cc: gregkh@linux-foundation.org Cc: dwmw@amazon.co.uk Cc: nickc@redhat.com Link: https://lkml.kernel.org/r/20180110224939.2695CD47@viggo.jf.intel.com Cc: Jiri Kosina jkosina@suse.cz Signed-off-by: Hugh Dickins hughd@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/tboot.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
--- a/arch/x86/kernel/tboot.c +++ b/arch/x86/kernel/tboot.c @@ -134,6 +134,16 @@ static int map_tboot_page(unsigned long return -1; set_pte_at(&tboot_mm, vaddr, pte, pfn_pte(pfn, prot)); pte_unmap(pte); + + /* + * PTI poisons low addresses in the kernel page tables in the + * name of making them unusable for userspace. To execute + * code at such a low address, the poison must be cleared. + * + * Note: 'pgd' actually gets set in pud_alloc(). + */ + pgd->pgd &= ~_PAGE_NX; + return 0; }
Patches currently in stable-queue which might be from hughd@google.com are
queue-4.9/kaiser-allocate-pgd-with-order-0-when-pti-off.patch queue-4.9/x86-pti-make-unpoison-of-pgd-for-trusted-boot-work-for-real.patch queue-4.9/kaiser-fix-intel_bts-perf-crashes.patch